Split items/ and trainers/ into their data/ and engine/ components

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/clefairy.asm

@@ -0,0 +1,10 @@
+; ClefairyPokedexEntry: ; 0x1824c8
+	db "FAIRY@" ; species name
+	dw 200, 170 ; height, weight
+
+	db   "Though rarely"
+	next "seen, it becomes"
+	next "easier to spot,"
+	page "for some reason,"
+	next "on the night of a "
+	next "full moon.@"